Stir sesame seeds in dry skillet over medium heat until aromatic and light golden, about 2 minutes. Transfer to small bowl to cool. Whisk next 6 ingredients in large bowl to blend. Add watercress, green onions, and jicama; toss to coat. Gently stir in avocados. DO AHEAD: Can be made 1 hour ahead. Cover; chill. Sprinkle salsa with toasted sesame seeds and serve chilled. *Available in the Asian foods section of some supermarkets and at Japanese markets.